w4 Luteal phase

Question 1

Phases of the luteal phase

Answer 1

Metoestrus and Dieostrus

TIme of ovulation until luteolysis of CL

Question 2

Luteal phase consists of

Answer 2

Luteinisation

Growth and development of CL

Luteolysis

Question 3

Luteinisation

Answer 3

Day 1-3

Transformation of follicle cells into luteal cells following ovulation (corpus haemorrhagicum)

Question 4

Growth and development of CL

Answer 4

Increase size and mass
Increase in progesterone production
From day 5 (diestris

Question 5

Luteolysis

Answer 5

Towards end of dioestrus
Destruction/lysis of CL
Lowers progesterone
Regress CL beocme corpus Albicans (white body) and scars for several cycles

Question 6

Stages of CL

Answer 6

Corpus Haemorrhagicum
-Bloody body, formed after ovulation - 1-3days

CL - yellow, starts growing day 3-5, produces P4

Corpus Albicans - white, remnants of CL, scar like, remain on ovary

Question 7

Luteinisation

Answer 7

Transoformation of theca interna and Granulosa to luteal cells

GOVERNED BY lh

Question 8

Steps of Luteinisation

Answer 8

Breakdown of basement membrane

Collapse of follicle into may folds
Folds interdigitate and mixing of thecal and granulosal cells

Formation of connective tissue networks

Angiogenesis - vascularisation of the CL

Question 9

Large luteal cells

Answer 9

COme from granulosa (20-40mirco mill

Produce progesterone

Undergo hypertrophy as CL develops - increase size

COntain oxytocin and relaxin

Question 10

Small Luteal cells

Answer 10

Thecal cells

Less than 20 micrmill
Produce progesterone
Undergo hyperplasia as CL develops (increase numbers

Question 11

Functionality of CL

Answer 11

Depends on Size
-Blood progesterone is correlated with size of CL

Degree of vascularisation
- ability of a CL to synthesise and deliver progesterone

Question 12

Target organs of progesterone

Answer 12

Hypothalamus
-Cause negative feedback (reduced basal GnRH pulse frequency)
-Prevents behavoiral oestrus
Prevents pre ovulatory LH surge

Uterus
-Stimulates endometrial gland secretion (supports development of conceptus)
Reduces myometrial tone

Mammary Gland
Promotes alveolar development in mammay gland

Question 13

Luteolysis

Answer 13

Loss of progesterone secretion by CL and luteal tissue mass

1-3 days at end of luteal phase

Irreversibe degeneration

Induced by PGF2a secreted by uterine endometrium

Question 14

Requirements of Luteolysus

Answer 14

Oxytocin receptors on endometrial cells

Presence of critcal level of oxytocin

PGF2a syntheses by endomedrium

Question 15

Oxytocyn

Answer 15

Released from large luteal cell granules

=increased PGF2a

Question 16

PGF2a

Answer 16

Secreted from endometrium

Reached ipsilateral ovary through vascular countercurrent mechanism in cow, ewe, sow (passive diffusion from uterine vein into the ovarian artery)
Counter current absent in mares (general circulation)

Question 17

PGF2a

Answer 17

can be used to artificially lyse the CL to synchronise oestrus and induce parturition

Question 18

Vascular counter current exchange

Answer 18

2 closely associated blood vessels flowing different ways
Low molecular wt substances can flow from one to another
PGF2a flows from uterine vein to ovarian artery
=no dilution through systemic circulation

Question 19

Mare PGF2a

Answer 19

systemic circulation

Question 20

Mechanisms of Luteolysis

Answer 20

Ischemia (reduced blood flow)

• PGF2a causes vasoconstricion of blood vessels supplying CL but its still adequta
• Capilary degeneration within CL is more likely

Cellular Mechanisms initiate apoptosis
-PGF2a binds to plasma membrane receptors on large luteal cells
Results in casade of events- activation og protein kinase c(PK-c) inhibits progesterone synthesis

Immune system
-inhibits progesterone synthesise by luteal cells